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<h2><a name="SECTION0033330000000000000000">
31.3.3 Examples</a>
</h2>

<p>
This section shows several simple examples of ASTs for Python source
code.  The examples demonstrate how to use the <tt class="function">parse()</tt>
function, what the repr of an AST looks like, and how to access
attributes of an AST node.

<p>
The first module defines a single function.  Assume it is stored in
<span class="file">/tmp/doublelib.py</span>. 

<p>
<div class="verbatim"><pre>
"""This is an example module.

This is the docstring.
"""

def double(x):
    "Return twice the argument"
    return x * 2
</pre></div>

<p>
In the interactive interpreter session below, I have reformatted the
long AST reprs for readability.  The AST reprs use unqualified class
names.  If you want to create an instance from a repr, you must import
the class names from the <tt class="module">compiler.ast</tt> module.

<p>
<div class="verbatim"><pre>
&gt;&gt;&gt; import compiler
&gt;&gt;&gt; mod = compiler.parseFile("/tmp/doublelib.py")
&gt;&gt;&gt; mod
Module('This is an example module.\n\nThis is the docstring.\n', 
       Stmt([Function(None, 'double', ['x'], [], 0,
                      'Return twice the argument', 
                      Stmt([Return(Mul((Name('x'), Const(2))))]))]))
&gt;&gt;&gt; from compiler.ast import *
&gt;&gt;&gt; Module('This is an example module.\n\nThis is the docstring.\n', 
...    Stmt([Function(None, 'double', ['x'], [], 0,
...                   'Return twice the argument', 
...                   Stmt([Return(Mul((Name('x'), Const(2))))]))]))
Module('This is an example module.\n\nThis is the docstring.\n', 
       Stmt([Function(None, 'double', ['x'], [], 0,
                      'Return twice the argument', 
                      Stmt([Return(Mul((Name('x'), Const(2))))]))]))
&gt;&gt;&gt; mod.doc
'This is an example module.\n\nThis is the docstring.\n'
&gt;&gt;&gt; for node in mod.node.nodes:
...     print node
... 
Function(None, 'double', ['x'], [], 0, 'Return twice the argument',
         Stmt([Return(Mul((Name('x'), Const(2))))]))
&gt;&gt;&gt; func = mod.node.nodes[0]
&gt;&gt;&gt; func.code
Stmt([Return(Mul((Name('x'), Const(2))))])
</pre></div>

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